Process for producing plastic containers



Sept. 12, 1967 K. R. ALLEN 3,341,644

PROCESS FOR PRODUCING PLASTIC CONTAINERS Original Filed July 29. 1959 2 Sheets-Sheet l 079 INVENTOR. 050

K 7282512 m dd, Leta {m Sept. 12, 1967 K. R. ALLEN PROCESS FOR PRODUCI Original Filed July 29. 1959 NG PLASTIC CONTAINERS 2 Sheets-Sheet 2 L w a? 3 I 2 (9 3.2 21/ 2Q JAWS/TOR 77777 37, A meihfi Qllem B /:Z&(,,/d 34' Fag Unite States Patent 3,341,544 patented Sept. 12, 1967 fiice This application is plication, Ser. No. 281,125, application is a continuation of my earlier application, Ser. No. 830,229, filed July 29, 1959.

This invention relates, in general, to ess for producing plastic containers.

While the container which will a continuation of my earlier apfiled May 17, 1963, which an improved proclimited to such use, but may be work as suitable and desired.

Prior plastic containers and schemes for producing same have been subject to various problems and shortcomings. For example, it has not been possible to obtain as uniform or as thin wall structure as desired, particularly where a plastic sheet made by extruding is blown or vacuum formed to shape. The wall of the finished container has not been as reinforced, and the containers have not been as completely adaptable for use in vending machines as desired.

Moreover, higher injection pressures have been required, and the forming cycle has not been as fast as desired, particularly in conventional injection molding.

According to the present invention, a plastic blank is formed of functionally diiferent parts of different wall thickness by injection molding of the plastic. More particularly, a plastic blank is formed having concentric portions for the rim, the side walls and the bottom wall of the finished container. The rim is relatively heavy and of a cross section and outline of substantially the rim of the finished container. The side wall portion of the preformed blank is of a thickness substantially greater than that of the side wall of the finished container. And more particularly, the bottom wall portion of the blank is of approximately the thickness of the bottom wall of the finished container.

The preformed blank, before it has cooled, or if cooled after the injection molding, after it is reheated, is transferred to the forming mold, and the central part of the blank is depressed by engagement of a plunger therewith to stretch the side walls and thin the same. Then, by pneumatic pressure diflierence, the stretched, or extended blank is pressed against the inner closed wall of the forming or container mold to the form of the finished container and to chill the plastic and set the same.

Advantages of the invention reside in the production of a container having a heavy reinforcing rim and more uniform and thinner wall structure. Moreover, a lower injection pressure is permitted, and a faster cycle is made possible than with conventional injection molding.

Another advantage is that a finished container is made without any additional operations, such as trimming containers from a sheet which has been vacuum formed to make such containers.

Numerous further advantages and adaptations of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings, it being understood that the invention is limited only within the scope of the appended claims and not to the particular embodiments selected for illustration.

In the drawings:

FIGURE 1 is a fragmentary sectional view illustrating injection mold parts and nozzle for making the plastic blank according to the present invention;

FIGURE 2 is a sectional View taken diagrammatically through the plastic blank formed in the injection mold of FIGURE 1;

FIGURE 3 is URE 2;

FIGURE 4 is a sectional view illustrating the mold back of FIGURE 1 applied to a forming mold and the a plan view of the blank shown in FIG- or extended by the plunger;

FIGURE 5 is a side elevational view of the container, partially in section, formed by pressing the stretched blank of FIGURE 3 against the wall of the forming mold;

FIGURE 6 is a fragmentary view, partially in section and partially in elevation, showing an alternative structure in which the plunger is not part of the injection mold and ring is employed in transferring the blank to the forming mold; and

FIGURE 7 is a fragmentary sectional view illustrating an alternative formation at the upper portion of the side wall of the cup.

Referring now to the The cavity 2 is formed in the injection mold back 4, and the injection mold front is shown at 5. The mold periphery of the mold A plunger 8 is disposed axially within the mold back 4. As shown, for example, in FIGURE 1, the plunger 8 has a head or flange 9 which, when the plunger is retracted fits in a correspondingly shaped recess 10 in the mold back 4. The plunger 8 is shown as having an axial bore or hole 11, and holes 12 opening radially from the inner cavity 2 is shaped to give the proper Wall distribution to the container when it is completed. The preformed blank 3 as formed in the cavity 2 has functionally different parts of diiferent wall thickness. More particularly, the blank 3 has concentric portions 13, 14 and 15 for the rim, the side walls and the bottom wall respectively of the completed cup or container.

A typical preformed blank is shown in FIGURES 2 and 3. The angle B and diameter D, as indicated in FIGURE 2, may be changed for different containers. Angle B maybe 1 and diameter D may be 2.875 inches for a 9 ounce container, as shown in FIGURE 5. The rirn portion 13 is heavy and of a cross section and outline of substantially the rim 13 of the finished container. The side wall portion 14 is of a thickness substantially greater than that of the side Wall 16 of the finished container. The bottom wall portion 15 is of a thickness substantially less than that of the side wall portion 14, and

approximately the thickness of the botom wall of the finished container.

1n FIGURE 2 the rim portion 13 is of a height of about .1- of aninch and of .a width of about .035 of an inch. The side wall portion 14 is of a thickness of about .095 of an inch adjacent to the rim .13 and tapers to a thickness of about .079 of an inch adjacent to the outer periphery of the bottom wall portion 15. The bottom wall portion 15 is of a diameter of 1 /8 inch and of a thickness of about .050 of an inch.

Upon completion of the preformed blank, the injection mold back 4 with the preformed blank 3 in the cavity 2 thereof is transferred to position over a forming mold 18, as illustrated in FIGURE 4.

The forming mold 18 is recessed at its upper end 19 to receive the mold back 4, and has a cavity ZOshaped to impart the desired shape to the cup or container. The cavity 20 may have annular ribs 41 to form correspondingly shaped annular ribs 22 on the side wall '16 of the finished container. The lower end of the cavity 20 is of reduced diameter at 21 to form a correspondingly reduced diameter portion 23 at the lower portion of the side wall of the container.

The container illustrated in FIGURE 5 has a diameter of 2% inches at the top of the rim 1 3 and a diameter of 2 inches .at the bottom of the reduced diameter portion 23. The height of this illsutrative container embodying the present invention is 3 /2 inches from the top of the rim 13 to the under surface 24 of the reduced diameter portion 23. The side wall of the reduced diameter portion 23 is shown as tapering upwardly from the bottom surface 24 to a lesser diameter at the bottom of the side wall portion thereabove. The ribs 22 may taper upwardly from their lower ends to lesser diameters at their upper ends.

The bottom surface of the finished cup or container may have three projecting legs, ni bs or prongs 26 formed integral therewith and equally spaced circumferentially. These projections 26 insulate the bottom of the cup from the surface of a table, or the like, to prevent injury thereto where, \for example, the cup contains hot coffee or other hot liquid.

The bottom of the rim 13 of the cup illustrated in FIGURE 5 forms an annular shoulder as indicated at 28.

In the cup illustrated fragmentarily at 29 in FIGURE 7, the annular shoulder 28' cor-responds with the annular shoulder 28 at the bottom of the rim 13 of the cup illustrated in FIGURE 5. nular projection 30 between the upper portion of therim 13 and the underlying side wall portion of the cup for use in stacking the cups, for example, in a vending machine.

The forming mold .18 has a moldfbottom'32 seating in a recess 33 in the bottom wall 34 of the mold 118, and provided with an integral axial part 35 projecting downwardly through an opening 36 in the bottom wall 34. A small annular gap 37 between the forming mold and the periphery of the mold bottom 32 allows air under the blank toescape where air is blown into the extended blank of plastic to force the plastic against the forming mold. The gap 37 opens out through radial holes 38 and an axial bore orhole 3-9 in the mold bottom 32.

Where vacuum is applied to the space 40 between the outer periphery of the sidewall of the extended blank and the wall of the forming mold, as shown in FIGURE 4, in conjunction with the blowing of air into the-interior of the extended blank, or in place of such blowing of air into the extended blank, the vacuum may be applied to the space 40 through the axial bore or hole 39 and the radial holes 38.

After transferring the injection mold back 4, with the preformed plastic blank 3 in the cavity thereof, to the container or forming mold 1 8, the preformed blank is brought to the form of the finished cup or container as follows:

The preformed blank may be molded into the form In this form of cup there is an anfrom position with the of the finished container before it has cooled or solidified after the injection molding of the blank, or it may be cooled after the injection molding, reheated and then formed into the container.

In eithercase, the plunger 8 is depressed or extended head 9 in the recess 10 to approximately the position illustrated in FIGURE 4.

The cooperation'of the head 9 of the plunger with the central or container bottom wall forming part 15 of the preformed blank, as the plunger is thus extended, mechanically depresses the central part of the blank and stretches or prestretches the .side wall portion 14 of the blank generally to extended form, as shown in FIGURE 4. The stretching of the side wall portion 14 of the blank, thins the same, but the bottom wall portion :15 remains approximatelythe thickness of the bottom wall of the finished container.

Then, by pneumatic pressure blank is pressed against mold 18 to bring the plastic blank to the form of the. finished container, and to chill the plastic and set. the

same.

The pressing of the stretched blank against the inner cold wall of the forming mold 18 may be accomplished by blowing air under pressure into the extended blank through the holes 11 and 12 in the plunger 10, or by applying vacuum to the space 40 through the holes 38 and 39 in the mold bottom 32, or by a combination of the two, i.e., blowing within the extended blank and applying vacuum to the exterior thereof.

The size of the plunger head 9 preferably approximates difference, the stretched the size of the bottom of the container, or the bottom wall forming portion 15 of the blank 3, although this may vary within the scopeof the present invention.

In the injection molding of the plastic blank, the plastic enters the injection mold at the center ofthe blank. Since this is the last place to fill in the injectionmold, the plastic is hottest at this point. In transferring the injection mold back 4, with the heated blank in the cavity thereof, to the forming mold, and blowing air into the extended blank, the plunger head or flange 9 shields the hot spot in the bottom wall forming portion of the blank, and

prevents the air from blowing through such hot spot.

wall forming portion 15 of the blank is vacuum is applied to the outside The hot bottom also protected where of the extended blank to press the same against the.

bring the plastic inner cold wall of the forming mold to to the form of the finished container and to chill the plastic and set the same.

The finished cup or container has a relatively heavy rim 13 which is advantageous, for example, in reinforcing the wall of the container and in dispensing and stacking the containers in a vending machine. The container produced according to the present invention has a more uni by blowing or. vacuum forming a plastic sheet made by extruding. Thinand better physical propform wall than is possible, for example,

not wall thickness is possible, erties are provided. Moreover, a lower injection pressure is permitted, and a faster cycle is possible than by conventional injection molding.

In FIGURE 6 the plunger 42 is not a part of the injection mold.'Instead, a ring 43 and clamping ring 44. are employed for transferring the preformed plastic bank 3' to the forming or container mold 18. The plunger 42 operates similarly to the plunger 8 and the parts of the mold 18' corresponding to parts of the mold 18 are designated by primed reference characters corresponding to the reference characters applied to the mold 18.

The embodiments of the invention disclosed in the drawings and specification are for illustrative purposes only,-and it is to be expressly understood that said drawings and thespecification are not to be construed as a definition of the limits or scope of the being had to the appended claims for that purpose.

the inner cold wall of the forming invention, reference alignment (a) said parison while still hot and (b) a blow mold cavity having side wall and bottom wall portions corresponding to size and contour to the side Wall and bottom wall portions, respectively, of the finished container, the parison projecting across the blow mold cavity in a plane substantially normal to the longitudinal axis of said cavity and said rim portion still being at least parbottom wall of said cavity, thereby (a) positioning said central portion of said parison adjacent its final position in said cavity, and (b) bringing said medial portion closer in contour and thickness to the side Wall portions of said container, while (c) the outer rim portion of the parison remains at least partially retained in said injection mold,

to a blowable shape; into full contact with said blow mold cavity without disturbing said rim portion in its still retained position; and finally removing the finished container side Walls and bottom wall from the blow mold and said container rim from its retained position in said injection mold.

2. In the method as defined in claim 1, the improvement of performing the injection molding step by injecting plasticized material into the injection mold at a location Within the confines of the central portion of said parison, so that the injection location is axially displaced prior to blowing, thereby subjecting the injection location to minimum stretching during blowing.

3. In the method as defined in claim 2, the further improvements of engaging the entire central portion of said parison with a plunger head and jointly displacing said plunger head and said central portion to an extent such that said central portion is confined between said plunger head and the blow mold bottom wall prior to blowing.

4. In a method of making an open-topped plastic container having a lip circumscribing the container top, a

0 ROBERT F. WHITE,

bottom wall and side wall, mold a substantially flat parison having (a) an outer rim corresponding in size and contour to the lip of the finished container, (b) a central portion corresponding substan tially in thickness and contour to at least a portion of said container bottom wall, and (c) a medial portion integrally joining said lip to said central portion, said medial portion being of a minimum thickness substantially greater than the thickness moving into axial parison and (b) a blow mold cavity having side wall and bottom wall portions corresponding to size and contour to the side wall and bottom wall portions, respectively, of the finished References Cited UNITED STATES PATENTS 688,924 12/ 1901 Blair. 2,317,763 4/ 1943 Hall. 2,331,688 10/1943 Hobson 26497 2,385,486 9/ 1945 Bartoe 264-331 2,789,312 4/1957 Borer. 2,854,694 10/1958 Mumford 26494 2,864,124 12/1958 Strauss. 2,878,513 3/ 1959 Slaughter. 2,977,637 4/1961 Thompson 264 292 X 3,011,216 12/1961 Gussoni 264-97 3,111,711 11/1963 Colombo 185 3,112,522 12/ 1963 Doyle 185 3,137,748 6/1964 Makowski 26497 3,162,706 12/ 1964 Cheney 264-97 Primary Examiner. R, B. MOFFITT, Assistant Examiner, 

1. IN A METHOD OF MAKING AN OPEN-TOPPED PLASTIC CONTAINER HAVING A LIP CIRCUMSCRIBING THE CONTAINER TOP, A BOTTOM WALL AND SIDE WALLS JOINING SAID LIP TO SAID BOTTOM WALL, THE STEPS OF (1) INJECTION MOLDING IN AN INJECTION MOLD A SUBSTANTIALLY FLAT PARISON HAVING (A) AN OUTER RIM PORTION CORRESPONDING IN SIZE AND CONTOUR TO THE LIP OF THE FINISHED CONTAINER, (B) A CENTRAL PORTION CORRESPONDING SUBSTANTIALLY IN THICKNESS AND CONTOUR TO AT LEAST A PORTION OF SAID CONTAINER BOTTOM WALL, AND (C) A MEDIAL PORTION INTEGRALLY JOINING SAID OUTER RIM TO SAID CENTRAL PORTION AND OF NEITHER THE THICKNESS NOR THE CONTOUR OF THE SIDE WALLS OF SAID CONTAINER, SAID MEDIAL PORTION BEING OF A THICKNESS SUBSTANTIALLY GREATER THAN THE THICKNESS OF SAID CONTAINER SIDE WALLS; (2) RELATIVELY MOVING INTO AXIAL ALIGNMENT (A) SAID PARISON WHILE STILL HOT AND (B) A BLOW MOLD CAVITY HAVING SAID WALL AND BOTTOM WALL PORTIONS CORRESPONDING TO SIZE AND CONTOUR TO THE SIDE WALL AND BOTTOM WALL PORTIONS, RESPECTIVELY, OF THE FINISHED CONTAINER, THE PARISON PROJECTING ACROSS THE BLOW MOLD CAVITY IN A PLANE SUBSTANTIALLY NORMAL TO THE LONGITUDINAL AXIS OF SAID CAVITY AND SAID RIM PORTION STILL BEING AT LEAST PARTIALLY RETAINED IN SAID INJECTION MOLD; (3) MECHANICALLY PUSHING THE CENTRAL PORTION OF SAID PARISON TOWARD THE BOTTOM WALL OF SAID CAVITY, THEREBY (A) POSITIONING SAID CENTRAL PORTION OF SAID PARISON ADJACENT ITS FINAL POSITION IN SAID CAVITY, AND (B) BRINGING SAID MEDIAL PORTION CLOSER IN CONTOUR AND THICKNESS TO THE SIDE WALL PORTIONS OF SAID CONTAINER, WHILE (C) THE OUTER RIM PORTION OF THE PARISON REMAINS AT LEAST PARTIALLY RETAINED IN SAID INJECTION MOLD, THUS (D) DEFORMING THE INITIALLY SUBSTANTIALLY FLAT PARISON TO A BLOWABLE SHAPE; (4) BLOWING THE SO DEFORMED PARISON INTO FULL CONTACT WITH SAID BLOW MOLD CAVITY WITHOUT DISTURBING SAID RIM PORTION IN ITS STILL RETAINED POSITION; AND (5) FINALLY REMOVING THE FINISHED CONTAINER SIDE WALLS AND BOTTOM WALL FROM THE BLOW MOLD AND SAID CONTAINER RIM FROM ITS RETAINED POSITION IN SAID INJECTION MOLD. 